1. Field of the Invention
The present invention relates to novel supported sequestering agents, with "supported sequestering agent" being defined as an agent capable of combining with various cations to form a complex therewith, said agent being covalently tethered to a support substrate.
The present invention also relates to the preparation of such novel sequestering agents, and to the use thereof in organic synthesis and for the extraction of various metals.
2. Description of the Prior Art
Known to this general art [compare Angew. Chem. Int., English Edition, 18, 421-429 (1979)], are polystyrene resins bearing quaternary ammonium groups having the structural formula: ##STR2## wherein R.sub.1, R.sub.2 and R.sub.3 are essentially alkyl radicals, and ##STR3## is the polystyrene backbone.
The principal disadvantage which limits the use of such resins on an industrial scale is, most notably, their lack of stability at temperatures in excess of about 100.degree. C.
In the aforenoted reference, there are also described certain "crown ethers" and "cryptants" grafted onto polystyrene backbones, the same being prepared by the reaction of appropriate amine derivative, the crown ether or the cryptant, with a chloromethyl polystyrene.
These substituted polymers, for example, those of the structural formulae: ##STR4## are much more useful than the aforesaid ammonium salts borne by polystyrene backbones by virtue of their greater activity and their better thermal stability. Nevertheless, there remain a certain number of disadvantages which do not favor their utilization on an industrial scale. Indeed, the crown ethers and cryptants are themselves compounds having highly sophisticated and complex molecular structures. It thus follows that the processes for the preparation thereof and their actual utilization are quite critical. Furthermore, their cost of production is extremely high. And these same disadvantages are multiplied on the level of the more complex macromolecules obtained after grafting same onto a polystyrene backbone.
The three types of products noted hereinabove have been tested in the prior art in nucleophilic substitution reactions by liquid/liquid phase transfer catalysis, such as in the halogen exchange reaction of bromooctane to 1-iodooctane and in nucleophilic substitution reactions by liquid/liquid phase transfer catalysis, such as, for example, in the reaction of benzyl chloride with alkaline acetates to yield benzyl acetate [Pure and Appln. Chem., 51, pp 2313-2330 (1979)].
Thus, serious need exists in this art for a novel class of sequestering agents which avoids those disadvantages and drawbacks above outlined.